# Can you charge a battery with another battery?

In summary: Some years ago it was discovered that certain sub C size NiCad cells performed better in RC cars and competition aircraft after they had been "zapped". The zapping process involved charging up a bank of capacitors the size of a shoebox and discharging them into the cell using an SCR the size of a hockey puck (I heard early experiments involved using a garden spade as a switch!). The wires connecting the capacitors to the cells would twitch due to the high current and Earth's magnetic field. A very high percentage of the cells survived.This is not something you would want to do at home. It's very dangerous. This is not something you would want to do at home. It's
To do this would you simply run the current from one battery through another in reverse? Would there be a significant loss in energy?

It is not impossible in general, but it can lead to bad consequences (including exploding batteries) if done improperly. Just don't do it.

To do this would you simply run the current from one battery through another in reverse? Would there be a significant loss in energy?

As mfb says, not directly. But there are battery-based battery chargers that have circuitry inside that makes the charging process safe and relatively efficient:

http://www.schoolmart.com/images/products/detail/EVOPowerPlusintocell.jpg
http://www.schoolmart.com/images/products/detail/EVOPowerPlusintocell.jpg

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berkeman said:
As mfb says, not directly. But there are battery-based battery chargers that have circuitry inside that makes the charging process safe and relatively efficient:

http://www.schoolmart.com/images/products/detail/EVOPowerPlusintocell.jpg
http://www.schoolmart.com/images/products/detail/EVOPowerPlusintocell.jpg
Ok, what about a capacitor charging a capacitor? And would charge be lost?

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Ok, what about a capacitor charging a capacitor? And would charge be lost?

Charge is conserved, but some energy is lost in the transfer of charge from one capacitor to another. In fact, it is a common FAQ to figure out where the energy goes...

berkeman said:
Charge is conserved, but some energy is lost in the transfer of charge from one capacitor to another. In fact, it is a common FAQ to figure out where the energy goes...
Ok lastly, what happens if you add two different quantities of charge with different voltages to a single capacitor? How would they come out in the discharge of the capacitor?

Ok lastly, what happens if you add two different quantities of charge with different voltages to a single capacitor?
That question does not make sense. You cannot "add a charge of X at voltage Y", the voltage is determined by the amount of charge and the capacitance (and it changes during the charging process).

berkeman
mfb said:
That question does not make sense.
sorry, If i charge a capacitor with a 12 volt battery for 30 seconds, then I charge it with a 9 volt battery for 30 seconds, what voltage will come back out of the capacitor? Hope that makes more sense.

what voltage will come back out of the capacitor?
It might be more relevant to ask how much smoke will come out of the battery.

Nugatory, billy_joule, e.bar.goum and 2 others
sorry, If i charge a capacitor with a 12 volt battery for 30 seconds, then I charge it with a 9 volt battery for 30 seconds, what voltage will come back out of the capacitor? Hope that makes more sense.

That depends on several factors, including the capacitance of the capacitor. If the capacitance is too small, then the capacitor is completely charged to 12 volts and connecting a 9-volt battery to it will probably damage the battery. If its very large then the 12v battery will not charge it to even 9 volts and you can then connect the 9v battery and charge it to 9v.

berkeman said:
Charge is conserved, but some energy is lost in the transfer of charge from one capacitor to another. In fact, it is a common FAQ to figure out where the energy goes...
Do we know where the energy goes?

Do we know where the energy goes?

Yes we do.

To do this would you simply run the current from one battery through another in reverse? Would there be a significant loss in energy?
You need higher potential to charge a battery. So if you are charging a 12V battery you would need 13-14V of any current throughput to charge that 12V bat.

There's some resistance and inductance in the circuit which can't be ignored when dealing with capacitors. If the inductance is negligible, then the RC product determines the charging or discharging time. With inductance, you can get damped oscillations.

berkeman said:
Yes we do.
Is there a way to calculate the energy lost through oscillations? If so can you show me or direct me to a link? Thanks for the help sir

MrAnchovy said:
It might be more relevant to ask how much smoke will come out of the battery.

Some years ago it was discovered that certain sub C size NiCad cells performed better in RC cars and competition aircraft after they had been "zapped". The zapping process involved charging up a bank of capacitors the size of a shoebox and discharging them into the cell using an SCR the size of a hockey puck (I heard early experiments involved using a garden spade as a switch!). The wires connecting the capacitors to the cells would twitch due to the high current and Earth's magnetic field. A very high percentage of the cells survived.

Do not try this at home! It's very dangerous.

## 1. Can you charge a battery by connecting it to another battery?

Yes, it is possible to charge a battery by connecting it to another battery. This process is known as "jumpstarting" and is commonly used for car batteries.

## 2. Is it safe to charge a battery with another battery?

In most cases, it is safe to charge a battery with another battery. However, it is important to follow proper safety precautions and make sure the batteries are compatible. Using the wrong type of battery or connecting them incorrectly can be dangerous.

## 3. What type of batteries can be used to charge another battery?

The type of battery that can be used to charge another battery depends on the specific batteries in question. In general, it is best to use a battery with a higher voltage and capacity than the one being charged. For example, a car battery can be used to charge a smaller battery, but not the other way around.

## 4. How long does it take to charge a battery with another battery?

The time it takes to charge a battery with another battery can vary depending on several factors, such as the capacity and voltage of the batteries, the charging method, and the condition of the batteries. In general, it can take anywhere from a few minutes to several hours.

## 5. Can you charge a completely dead battery with another battery?

In most cases, it is possible to charge a completely dead battery with another battery. However, it may take longer and may not be as effective as using a proper battery charger. It is important to make sure the dead battery is compatible with the battery being used to charge it and to follow proper safety precautions.

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